It is natural that children are curious about the world around them.For example,they want to
know how their hearts beat.They want to know why the ocean water tastes salty.
As children grow up,they become curious about different kinds of things.When they are babies,
they are interested in the parte of their bodies and in the smiles of their mothers.Then they become interested in the physical world around them:the plants,the animals,and the sky.Later,they
become interested in the things that people have made:wheels,bicycles,cars.And when they are nules,theirecuriosity econtinues,Sometimes huis curoeily leaulk to a curer in sciemnce.
Scientists spend their lives trying to find out about the world.Thoe who work with the earth
ociences study the earth,the ceans,and the akies.Other aeiemtins who touly loring lhinge work wilh the biological sciences.A thicd goup of scientistk audy the phywical wieces,e g phyuice,
chemistry.These scientists have already discovered a lot about our world.For example,they lell us why your heaurt beats fast when you run.They say thet when you are quiet,your heart normlly beats sixty-five or scventy-five times a minute.Your heart is a pump(泵）that pumps bloud to all parte of the body.The blood carries oxygen and nutrition.When you run,your muscles work very hard and use the nutrition that the blood carries to them.The muscles need oxygen,too.So your bruin sends a signal to the heart.The signal means that the muscles need more nutrition and oxygen.Then the heart beats fast and sends blood quickly to the muscles.It may beat 90 to 140 times a minute. Of course,scientists cannot answer all of our questions.If we ask,"Why does the ocean water taste salty"scientists will say that the salt comes from rocks.When a rock gets very hot or very cold,it cracks.Rain falls into cracks.The rain then carries the salt into the earth and into the rivers.The rivers carry the salt into the ocean.But then we ask,"What happens to the salt in the ocean?The ocean does not get saltier every year,"scientists are not sure about the answer to this question. We know a lot about our world,but there are still many answers that we do not have,and we are curious.
51.According to the text,which of the following statements is true?
A.People are curious in almost the same way.
B.People in different countries are interested in different things.
C.Men and women are curious about different things.
D.People of different ages are interested in different things.
52.Scientists who work with the biological sciences study
B.the earth,the oceans and the sky
A.ocean water
C.plants and animals
D.man-made things
53.When you run,your muscles need
B.water
A.more nutrition and oxygen
D.more signals
C.more salt
54.A rock cracks
A.when rain falls onto it
B.in dry regions
C.at very high or very low temperatures
D.when salty water falls in it
55.People are always curious about the world because
A.they cannot explain many things
B.they know nothing about the world
C.they know little about the world
D.they want to be scientists
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